Prosthetic implant

ABSTRACT

An implant is provided for which has an outer bearing surface and an inner attachment surface. The outer bearing surface functions as ajoint contact surface for a reconstructed bone joint. The inner attachment surface contacts a bone and is attached thereto. The inner attachment surface of the implant is curvilinear from the anterior to the posterior area of the femur, and is also curvilinear from the medial to the lateral areas of the femur to approximates the shape of natural femur. The resection of the femur for accommodating the implant can be properly performed by a milling device employing one or more curvilinear milling bits.

RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/892,286, filed Jul.14, 1997 now U.S. Pat. No. 5,879,354, which was a divisional of U.S.patent application Ser. No. 08/649,465, filed May 17, 1996, now U.S.Pat. No. 5,755,803, which was a continuation-in-part application of U.S.patent application Ser. No. 08/603,582, filed Feb. 20, 1996, now U.S.Pat. No. 5,810,827 which was a continuation-in-part application of U.S.patent application Ser. No. 08/300,379, filed Sep. 2, 1994 by Goldsteinet al., now U.S. Pat. No. 5,514,139, dated May 7, 1996.

U.S. patent application Ser. No. 08/603,582, filed Feb. 20, 1996, nowU.S. Pat. No. 5,810,827, is also a continuation-in-part application ofU.S. Ser. No. 08/479,363, filed Jun. 7, 1995, now U.S. Pat. No.5,643,272 which is a continuation-in-part of U.S. patent applicationSer. No. 08/342,143, filed Nov. 18, 1994 by Haines et al., now U.S. Pat.No. 5,597,379, which is a continuation-in-part application of U.S.patent application Ser. No. 08/300,379, filed Sep. 2, 1994, byGoldstein, et al., now U.S. Pat. No. 5,514,139, dated May 7, 1996. U.S.Ser. No. 08/479,363, now U.S. Pat. No. 5,643,272 is also acontinuation-in-part of U.S. Ser. No. 08/300,379, Sep. 2, 1994, now U.S.Pat. No. 5,514,139. U.S. Ser. No. 08/603,582, now U.S. Pat. No.5,810,872 is also a continuation-in-part application of U.S. Ser. No.08/342,143 now U.S. Pat. No. 5,597,379 which is a continuation-in-partapplication of U.S. Ser. No. 08/300,379 now U.S. Pat. No. 5,514,139.

The entire disclosures of these related applications are expresslyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a prosthetic apparatus foraugmenting a musculoskeletal structure for maintaining or improving saidstructure, and more particularly to a prosthetic implant for use inreconstructed or replacement knees or other joints.

2. Related Art

Different apparatus have been developed to enable a surgeon to replacedamaged osseous and/or articular material of the muscoskeletal structurewith prosthetic devices or structures in order to preserve or restorethe structural or kinematic function of the body. Keeping in mind thatthe ultimate goal of any surgical procedure is to restore the body tonormal function, it is critical that the quality and orientation of anybone cuts, as well as the quality of fixation, and the location andorientation of objects or devices attached to the bone, is sufficient toensure proper healing of the body, as well as appropriate mechanicalfunction of the musculoskeletal structure.

While the implant of the present invention has applications throughoutthe human body, the applications and embodiments shown and describedherein are specifically configured for total knee replacement, asurgical procedure where planar or curvilinear surfaces are created inor on bone to allow for the proper attachment or implantation ofprosthetic devices. It should be noted that the apparatus and methodsset forth herein can modified and applied to any form of jointreplacement wherein the function to be restored is dictated by bothstatic and dynamic principles, as well as forms of muscoskeletalreconstruction which are dictated primarily by static principles ofoperation.

Currently, bony surfaces to be resected or cut are done so in a seriesof planar surfaces. In total knee replacement, a series of curvilinearsurfaces or resections are created in the bone to allow the attachmentof a number of prosthetic devices to the femur, tibia, and patella. Inthe case of the femur, the posterior and distal femoral condyles, theanterior femoral cortex, and other anatomic features are referenced todetermine the location and orientation of the resections. The locationand orientation of these resections are critical in that they dictatethe quality of fixation of the prosthesis to the bone, as well as thefinal location and orientation of the prosthesis.

There are several major problems inherent in current implant designscaused directly by the need for interior and predominantly planarfixation surfaces (these surfaces are interior surfaces of the implantwhich mate with the resected bone) embodied in implant designs whoseexternal geometry is predominantly curvilinear. These problems include:

a. the removal of excessive amounts of viable osseous tissues;

b. non-optimal or “unnatural” patellofemoral kinematics;

c. excessive implant rigidity resulting in stress shielding of livingbone;

d. stress risers at the vertices of the planar fixation surfaces of theimplant leading to potential failure sites under fatigue loading, and

e. excessively massive implants resulting in additional material costs.

Past efforts have not been successful in properly addressing theseconcerns. Such previous efforts at implants are set forth in thefollowing patents, none of which teach or suggest all of the benefitsand advantages of the present invention. These previous patents include:

Goodfellow, et al., U.S. Pat. No. 5,314,482, discloses a femoral implanthaving a convexly shaped spherical articulation surface and a securementsurface having major and minor areas at opposite end portions. The majorarea is essentially concavely spherically concentric with the articularsurface to form a shell body part. The minor area is essentially planarand extends chordally of the articulation surface. The implant furtherincludes a bone-penetrating pin extending radially from the major areain a direction parallel to the longitudinal direction of the minor area.

Walker, et al., U.S. Pat. No. 4,822,365, discloses a method of designinga prosthesis having convex male and concave female portions. The surfaceof the condylar male portion of the prosthesis is generated by analysisof either an average or specific condyle, or a distortion thereof to fitobserved general dimensions of a specific patient. The female surfaceincludes flexion and laxity surfaces. The flexion surfaces are generatedby plotting the path of articulation of substantial points of contactbetween the male portion and a corresponding female portion. The laxitysurfaces comprise raised guide-bearing surfaces for resistingdislocation of the condylar portion.

Hanslik, et al., U.S. Pat. No. 4,770,663, discloses a knee jointendoprosthesis comprising a femur with two skid surfaces and a spacetherebetween. The skid surfaces are interconnected at a front end. Theskids having a curvature increasing from the front end to a rear end.The skids are also curved on planes perpendicular to the curvature. Thejoint endoprosthesis further comprises a tibia component having twosurfaces on which the skids ride.

Zichner, et al., U.S. Pat. No. 4,662,889, discloses a knee jointprosthesis having a C-shaped a femur cap for attachment to a resectedfemur condyle. The cap includes an aperture therethrough for receiving ashaft. A cap is also placed over the tibia. A connecting member isimplanted into the tibia and interconnected with the femur by the shaft.

Shoji, et al., U.S. Pat. No. 4,586,933, discloses a knee implant havinga femoral component with a curved articulating surface, movable insertspositioned between the femoral component and a tibial tray, the insertshaving concave articulating surfaces at the top and bottom thereof, anda tibial tray with convex tracks and posterior stops.

Johnson, et al., U.S. Pat. No. 4,568,348, discloses a knee prosthesishaving a femoral component for attachment to the femur, a tibialcomponent for attachment to the tibia and a meniscal componentpositioned therebetween. The tibial component has a concave bearingsurface. The meniscal component has bearing surfaces complimentary tothe tibial component and the femoral component. The femoral componenthas a two-part curved bearing surface including a first curved portionand a second curved posterior portion contiguous with and of relativelylesser curvature than the first curved portion.

Schurman, et al., U.S. Pat. No. 4,358,859, discloses a knee prosthesiscomprising a femoral implant having a condyle section and a stem, and atibial implant having a tibial plateau and a stop plate and a stem.

Forte, et al., U.S. Pat. No. 4,353,135, discloses a knee implant havinga patellar flange comprising a curved base and a pair of condylarrunners.

Russell, et al., U.S. Pat. No. 4,722,330, discloses a distal femoralsurface guide for mounting on an intramedullary alignment guide for usein shaping the distal femoral surface. A conventional shaping means suchas an oscillating saw or hand saw is introduced into slots in thesurface guide to resect the femur. The device also includes stabilizingmembers that extend along the sides of the femur to stabilize thedevice. The attachment surface of the implant comprises a series ofplanar surfaces.

Lackey, U.S. Pat. No. 5,053,037, discloses a femoral drill guide withinterchangeable femoral collets, a femoral reamer and a femoralanterior/posterior cutting block with an adoptable anterior femoralledge. A plurality of diagonal slots are provided for making diagonalcuts in the distal end of the femur. The attachment surface of theimplant comprises a series of planar surfaces.

Ferrante et al. U.S. Pat. No. 5,098,436, discloses a modular guide forshaping a femur comprising a first bracket defining a generally U-shapedstructure having an internal surface adapted to be seated on the distalaspect of a resected femur bone and an elongated central openingappointed to expose a selected area of the resected femur, including acurved track for guiding a first shaping tool along a predetermined pathfor controlled shaping of a curved patellar groove and a portion of theselected area exposed through the opening. A second bracket defines alinear slotted bore extending generally parallel to the long axis of thefemur for guiding a second shaping tool to form a relatively deep recessaccommodating an intercondylar-stabilizing housing of a knee implant.

Poggie, et al., U.S. Pat. No. 5,250,050 discloses an apparatus for usein preparing the bone surfaces for a total knee prothesis, comprisingcutting guides, templates, alignment guides, a distractor and clampinginstruments. The instrument for alignment of the cutting surface forresecting the tibia includes an ankle clamp, an adjustable alignmentrod, and a cutting platform. After the cutting platform is properlyaligned on the tibia, it is pinned thereto and the tibia may be resectedusing an oscillating saw. Also disclosed is a patella resection guidecomprising a scissor-type clamp having distal gripping arms, each ofwhich define a cutting surface, and gripping teeth. The attachmentsurface of the implant comprises a series of planar surfaces.

Caspari, et al., U.S. Pat. Nos. 5,263,498, 5,228,459, and 5,304,181disclose a method and apparatus for orthoscopically preparing bonesurfaces for a knee replacement. A tibial jig is attached to the tibiaat just above the ankle at a lower end and to just below the tibialtubercle at an upper end. One portal is formed in the knee for insertionof an orthoscope for viewing the knee, and another portal is formed forintroducing resecting instruments. A cutting platform is aligned andsecured in position and a cutting module is attached. Initially, aplunge cut across the tibial eminence is produced. This procedure isrepeated until the surface of the tibial plateau is covered with trailshaving ridges therebetween. Thereafter, the device is passed back andforth over the tibial plateau to remove the ridges. The attachmentsurface of the implant comprises a series of planar surfaces.

Whiteside, U.S. Pat. No. 4,474,177 describes instruments for creatingthe distal femoral surfaces where a guide is used to index a flatsurface used to guide the distal femoral resection. The attachmentsurface of the implant comprises a series of planar surfaces.

Kaufman, et al. U.S. Pat. No. 4,721,104 describes a method of preparingthe intracondylar area of the distal femur. The attachment surface ofthe implant comprises a series of planar surfaces.

Collomb, European Application No. 538153-A1, discloses a modular devicefor positioning a knee prosthesis on a bone. The attachment surface ofthe implant comprises a series of planar surfaces.

Bert, et al., U.S. Pat. No. 5,234,433, discloses a method and apparatusfor unicompartmental total knee arthroplasty. The attachment surface ofthe implant comprises a series of planar surfaces.

Pynaov, Russian Application No. 577,020, discloses an instrument forshaping the end joint of a bone to prevent arthrosis and ankylosis. Theinstrument is used to remove a central portion of the joint so that thejoint ends are contacted in one plane without causing irritation in thepara-articular tissues. No implant structure is disclosed.

None of these previous efforts, however, disclose all of the benefitsand advantages of the present invention, nor do these previous patentsteach or suggest all the elements of the present invention.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide an apparatusto properly replace damaged bony tissues.

It is also an object of this invention to provide an apparatus toproperly replace damaged bony tissues in joint replacement surgery.

It is also an object of the present invention to provide an implant forthe attachment to a distal femur in the context of knee replacementsurgery.

It is an additional object of the present invention to provide a methodand apparatus for making a curvilinear implant.

It is another abject of the present invention to provide an implanthaving a reduced thickness to reduce the amount of material required tomake the implant.

It is even another object of the present invention to provide an implanthaving curvilinear fixation surfaces for increasing the strength of theimplant.

It is another object of the present invention to provide an implanthaving a fixation surface that is anterior-posterior curvilinear andmedio-lateral curvilinear.

It is another object of the present invention to provide an implant thathas a fixation surface that is shaped to resemble a natural distalfemur.

It is also an object of the present invention to provide an implantapparatus for allowing proper patellofemoral articulation.

It is a further object of the present invention to provide for minimalstress shielding of living bone through reduction of flexural rigidity.

It is an additional object of the present invention to provide animplant apparatus having internal fixation surfaces which allow forminimal bony material removal.

It is another object of the present invention to provide an implantapparatus with internal fixation surfaces that minimize stress risers.

It is another object of the present invention to provide an implantapparatus having internal fixation surfaces for precise fixation tocurvilinear body resections.

It is another object of the present invention to provide an implantapparatus having internal fixation surfaces for precise apposition tocurvilinear body resections.

It is another object of the present invention to provide an implantapparatus having internal fixation surfaces for curvilinear interiorfixation geometries closely resembling the geometry of the external orarticular geometry of the implant apparatus.

It is also an object of this invention to provide a method and apparatusfor properly locating and orienting a prosthetic implant with respect toa bone.

It is another object of the present invention to provide an implantwhich is simple in design and precise and accurate in operation.

It is also an object of the present invention to provide an implantwhich minimizes the manual skill necessary to complete the procedure.

It is still yet another object of the present invention to provide animplant which minimizes the amount of bone removed.

It is even another object of the present invention to provide a methodand apparatus for removing material from a bone such that both thecutting path and cutting profile are predominantly curvilinear.

These objects and others are met by the implant of the present inventionwhich has an outer bearing surface and an inner attachment surface. Theouter bearing surface functions as a joint contact surface for thereconstructed bone. The inner attachment surface contacts a bone and isattached thereto. The inner attachment surface of the implant iscurvilinear from an anterior to a posterior area of the femur, as isconventionally known, and is also curvilinear from a medial to a lateralarea of the femur to approximate the shape of natural femur. Theresection of the femur for accommodating the implant can be properlyperformed by a milling device employing one or more curvilinear millingbits.

There are numerous advantages associated with the curvilinear implant ofthe present invention. First, it will allow for a very thin implantcross-section and therefore necessitate the removal of the least amountof viable osseous tissue. Accordingly, the kinematics of the artificialjoint could be made to be as close as possible to that of a healthy,natural knee joint. In addition, the curvilinear geometry of the implantdramatically decreases the stress risers inherent in conventionalrectilinear femoral implants and allows for a thinner cross-sectionalgeometry while potentially increasing the resistance of the implant tomechanical failure under fatigue or impact loading. Conversely, thecurvilinear geometry of the implant may also allow for an advantageousreduction in the flexural rigidity of the implant which may result inavoidance of the “stress-shielding” inherent in rigid implant designs.

This curvilinear implant of the present invention could also result in aless expensive femoral implant because of the reduced amount of materialneeded for the implant, as well as an improved, more natural, and evenstronger knee replacement. The cross-section of the implant could bevaried to assist in seating the implant and to increase the strength andfit of the implant. The implants of the present invention havingcurvilinear implant surfaces could be fabricated of metal, plastic, orceramic or any other material. Further, the thickness of the implantsand the material required to fabricate the implant could be reduced asthe implants are adapted to increasingly curvilinear surfaces.

The resected surfaces of a femur or other bone to accept the implant ofthe present invention could be prepared by the apparatus and method forresection shown and described in the prior related applications setforth herein, the entire disclosures of which are expressly incorporatedherein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Other important objects and features of the invention will be apparentfrom the following Detailed Description ofthe Invention taken inconnection with the accompanying drawings in which:

FIG. 1 is a perspective view of a femoral implant of the presentinvention having a curvilinear implant fixation surface.

FIG. 2 is a side plan view of the femoral implant shown in FIG. 1, FIGS.2A, 2B, 2C and 2D being sectional views taken along lines A—A, B—B, C—Cand D—D of FIG. 2, respectively.

FIG. 3 is a perspective view of a curvilinear milling bit and resectionguide for creating a curvilinear resection in a bone for accepting thecurvilinear implant shown in FIG. 1.

FIG. 4 is a side plan view of the curvilinear milling bit and resectionguide shown in FIG. 3.

FIG. 5 is a perspective view of another embodiment of a milling bit forcreating a resection in a bone for accepting the curvilinear implant ofthe present invention.

FIG. 6 is a side plan view of another embodiment of the femoral implantshown in FIG. 1.

FIG. 7 is a front plan view of another curvilinear milling bit forcreating a curvilinear resection in a bone for accepting the curvilinearimplant shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The particular example of the present invention discussed herein relateto a prosthetic implant for attachment to a femur in the context oftotal knee arthroplasty, i.e. a femoral implant. However, it should bepointed out that the principles described herein may be applied to anyother applications where foreign or indigenous material is affixed toany other anatomic feature.

As shown generally in FIGS. 1 and 2, the implant apparatus of thepresent invention, generally indicated at 10, comprises curvilinearinterior fixation surface 20 as well as curvilinear exterior bearingsurface 40. Importantly, the implant of the present invention includescurvilinear surfaces extending from an anterior to a posterior area ofthe femur and/or implant, as is conventionally known, as well ascurvilinear surfaces extending from a medial to a lateral area of thefemur and/or implant to approximate the shape of natural femur. In otherwords, the fixation path (i.e. corresponding to the cutting path alongwhich the milling bit rides to resect the femur; indicated by arrow A inFIG. 1) as well as the fixation profile (as one proceeds along thecutting profile orthogonally to the cutting path; indicated by arrow Bin FIG. 1) are both predominantly curvilinear. As such, the cuttingprofile (arrow B) of the interior fixation surface 20 could include acurved or flat 22 and another curved or flat area 24 therebetween.Preferably, the outer areas 22 are flat or relatively flat and the innerarea 24 is curved to approximate the shape of a natural distal femur 12.It should be pointed out the outer areas 22 could be curved, and theinner area 24 could also be curved, but embodying differing radii ofcurvature. Additionally, it should be pointed out the geometry of theinternal fixation surface 20 of the implant 10 could be varied asdesired. As such, any combination of flat surfaces and curvilinearsurfaces could be used. As shown in FIG. 2, and in more detail in FIGS.2A, 2B, 2C and 2D, the cross-sectional thickness and medio-lateral widthof the implant of the present invention could vary along the implant 10.This variance results from merging a cutting tool to cut a bone, i.e.,the implant 10 closely resembles in size and shape the material removedfrom the bone. Accordingly, the cut starts as a point 25 and grows indepth and width.

The curvilinear bone surfaces necessary for proper fixation of such animplant 10 may be generated through the use of the curvilinear millingbit or form cutter and the curvilinear cutting path means discussed inthe previous related applications set forth herein, the entiredisclosures of which are expressly incorporated herein by reference.Basically, the milling bit has a profile resulting in form cutterconfiguration which is concentric about its longitudinal axis to effecta curvilinear cutting profile for receiving the implant of the presentinvention. One embodiment of such a form cutter is shown in FIGS. 3 and4. While it is possible to use multiple form cutters with differinggeometries and therefore an implant 10 with an internal geometry thatvaries along the cutting path from the anterior to the posterior of afemur, for the sake of intraoperative time savings, a singleanatomically optimal form cutter is preferable.

The form cutter shown in FIGS. 3 and 4 comprises a cutting guide 80having a cutting paths 82 interconnected by member 81. A milling bit 90having cylindrical milling areas 92 at the ends, and a curved millingarea 94 at the center could be used. Of course, the milling areas carrycutting teeth. Spindles 91 interconnected at each end of the milling bit90 could engage and ride the cutting path 82 of the cutting guide 80.The milling bit 90 is then guided along the cutting path 82 by means ofa handle. Importantly, the shape of the milling bit 90 could be variedas desired to create a resection having a desired cutting path as wellas a desired cutting profile.

The medio-lateral cross-sectional internal geometry of such an implant10, and therefore the necessary resected bony surfaces of the femur, areconsistent about the cutting path in a single form cutter system. Itshould be noted that the implant 10 may possess a notch 60 betweenmembers 62 (posterior femoral implant condyles) in the areasapproximately between the distal and posterior femoral condylar areas toaccommodate the posterior cruciate ligament, as well as for otherreasons. Because of the notch 60 between the posterior femoral condyles,the form cutter may not cut any material in the notch 60.

Additionally, it may be advantageous to utilize a secondary form cutteras shown in FIG. 5 for use in creating a slot or slots in or near thedistal area of the femur before or after it has been resected. Such asecondary cutter 70 would include engagement means 72 for engagementwith driving means, and a shaft 74 carrying one or more cutters 76 forcutting slots into the femur through one or more of the resectedsurfaces thereof.

Through the inclusion of an additional or adjunct cutting path in thepattern means, it would be advantageous to utilize the form cutter tocreate the aforementioned slots in the distal femur to accommodate thefixation fins which may be molded as an integral part of the interiorsurface of the implant 10. An implant with fixation fins is shown inFIG. 6. The fins 28 would provide medio-lateral fixation stability inaddition to that provided by the trochlear groove geometry of theimplant 10. Further, the fins also provide for additional surface areafor bony contact and ingrowth to increase implant fixation both incemented and cementless total knee arthroplasty.

FIGS. 7 shows another embodiment of a milling bit, generally indicatedat 190 for creating a curvilinear cutting path and curvilinear cuttingprofile in femur 12. In this embodiment, the transition from a firstcutting area 192 to a second cutting area 194 is continuous and smooth.This milling bit 190 also includes spindles 191 at the ends thereof forengagement with pattern means to guide the milling bit along a cuttingpath.

There are numerous advantages to the femoral component herein described.Foremost, it will allow for the thinnest implant cross-section possible(perhaps 3 mm to 6 mm in nominal thickness) and therefore necessitatethe removal of the least amount of viable osseous tissue. This isespecially critical in situations where the probability of revisionsurgery is high and the amount of viable bone available for revisionimplant fixation and apposition is a significant factor in the viabilityof the revision procedure. Since the form cutter configuration allowsfor similar amounts of tissue to be removed from the trochlear groove,the bony prominences surrounding the trochlear groove, the femoralcondyles, and the other articular surfaces of the femur, the externalgeometry of the femoral implant can be optimized for patellofemoralarticulation as well as tibiofemoral articulation. In essence, thekinematics of the artificial joint could be made to be as close aspossible to that of a healthy, natural knee joint.

In addition, the curvilinear geometry of the implant dramaticallydecreases the stress risers inherent in conventional rectilinear femoralimplants and allows for a thinner cross-sectional geometry whilepotentially increasing the resistance of the implant to mechanicalfailure under fatigue or impact loading. The implant could have arelatively consistent cross-sectional thickness throughout the implant,or it could be varied as desired.

The curvilinear geometry of the implant may also allow for anadvantageous reduction in the flexural rigidity of the implant which mayresult in avoidance of the “stress-shielding” inherent in rigid implantdesigns. Stress shielding being a phenomenon that may occur when livingbony tissue is prevented from experiencing the stresses necessary tostimulate its growth by the presence of a stiff implant. This phenomenonis analogous to the atrophy of muscle tissue when the muscle is notused, i.e. when a cast is placed on a person's arm the muscles in thatarm gradually weaken for lack of use.

Further, the curvilinear implant of the present invention could allowfor the use of a ceramic material in its construction. Since ceramicsare generally relatively weak in tension, existing ceramic implantdesigns contain very thick cross-sections which require a great deal ofbony material removal to allow for proper implantation. Utilization ofceramics in the curvilinear implant would not only allow for thesuperior surface properties of ceramic, but also avoid the excessivelythick cross-sections currently required for the use of the material.

The curvilinear implant of the present invention could result in a lessexpensive femoral implant because of the reduced amount of materialneeded for the implant, as well as an improved, more natural, and evenstronger knee replacement. It may desirable to vary the cross-section ofthe implant to assist in seating the implant, to increase the jointkinematics and to increase the strength and fit of the implant. Theimplant of the present invention could be fabricated of metal, plastic,or ceramic or any other material or combination thereof. Further, thethickness of the implants and the material required to fabricate theimplant could be reduced as the implants are adapted to increasinglycurvilinear surfaces. Also, it should be pointed out that such implantswith curvilinear implant surfaces require less bone to be removed toobtain a fit between the implant and the bone. Finally, it should benoted that curvilinear milling bits hereinbefore described would workwell for preparing a bone to receive an implant with curvilinearinterior implant surface.

Importantly, by using a milling bit having a curved profile, one can cuta femur to resemble the natural shape of the femur, i.e. the resectedfemur would include condylar bulges and a central notch. This wouldreduce the amount of bony material that must be removed from the femurwhile maintaining the structural integrity of the femur. Of course, anyprosthetic implant used for attachment to a femur resected by the curvedprofile milling bit would necessarily have an appropriately contouredinner fixation surface for mating with contoured surface of the femur.Additionally, it should be noted that the curved profile milling bitcould have one or more curvilinear bulges along the length thereof asshown in FIGS. 3 and 4, or alternatively, could have one or more bulgesdiscretely formed along the length thereof

Modifications of the foregoing may be made without departing from thespirit and scope of the invention. What is desired to be protected byLetters Patents is set forth in the appended claims.

What is claimed is:
 1. A prosthetic implant for attachment to a resectedfemur for total knee arthroplasty comprising: an outer bearing surfacehaving a three dimensionally curved geometry and including a patellargroove; an inner contact surface having a three dimensionally curvedgeometry, said geometry curved along a medio-lateral direction and ananterior-posterior direction; said inner contact surface including aninner patellar groove area, said inner patellar groove area being of athree dimensionally curved geometry, said geometry curved along amedio-lateral direction and an anterior posterior direction; and saidinner contact surface geometrically corresponding to a geometry of aresected femur having a three dimensionally curved geometry, for fullcontact and attachment of said inner contact surface with a resectedfemur.
 2. The implant of claim 1 wherein the inner contact surfacegeometrically approximates the outer bearing surface.
 3. The implant ofclaims 1 wherein the inner contact surface geometrically matches theouter bearing surface.
 4. The implant of claim 1 wherein the innercontact surface approximates the geometry of a non-resected bone to bereconstructed.
 5. The implant of claim 4 wherein the inner contactsurface fully contacts the curved surfaces of a bone are formed by atleast one milling bit having a curvilinear profile.
 6. The implant ofclaim 1 wherein the anterior-posterior curvature of the inner contactsurface varies along the implant to approximate the geometry of a bone.7. The implant of claim 1 wherein the thickness of the implant betweenthe outer bearing surface and the inner contact surface is uniform forthe implant.
 8. The implant of claim 1 wherein fins are interconnectedwith the inner contact surface of the implant.
 9. A prosthetic implantfor attachment to a resected bone comprising: an outer bearing surface;an inner contact surface including inner medial and lateral condylarareas; each of said inner medial and lateral condylar areas being of athree dimensionally curved concave geometry, said concave geometrycurved along a medio-lateral direction and an anterior-posteriordirection; each of said inner medial and lateral condyle areasinterconnected by an inner patellar groove area, said inner patellargroove area being of a three dimensionally curved convex geometry, saidconvex geometry curved along a medio-lateral direction and an anteriorposterior direction; and said inner contact surface geometricallycorresponding to a geometry of a resected femur having a threedimensionally curved convex medial and lateral condylar geometry, and athree dimensionally curved concave patellar groove geometry, for fullcontact and attachment of said inner contact surface with a resectedfemur.
 10. The implant of claim 9 wherein the inner contact surfacegeometrically approximates the outer bearing surface.
 11. The implant ofclaims 9 wherein the inner contact surface geometrically matches theouter bearing surface.
 12. The implant of claim 9 wherein the innercontact surface approximates the geometry of a non-resected bone to bereconstructed.
 13. The implant of claim 9 wherein the inner contactsurface fully contacts the curved surfaces of a bone are formed by atleast one milling bit having a curvilinear profile.
 14. The implant ofclaim 9 wherein the anterior-posterior curvature of the inner contactsurface varies along the implant to approximate the geometry of a bone.15. The implant of claim 9 wherein the thickness of the implant betweenthe outer bearing surface and the inner contact surface is uniform forthe implant.
 16. The implant of claim 9 wherein fins are interconnectedwith the inner contact surface of the implant.